1. Field of the Invention
The present invention relates to an image processing apparatus, and more particularly to an image processing apparatus capable of reproducing an image with visually natural contrast.
2. Description of the Prior Art
In apparatus for producing a hard copy of an image in response to image signals received from an input device such as a television camera or a CCD sensor, the contrast of the image signals has conventionally been corrected according to the following formula: EQU X.sub.1 =aX+B (1)
In this manner the correction of the contrast is achieved by multiplying and adding constant correction parameters a, B to the input signal X.
However human vision is unable to follow such correcting method.
Such phenomenon will be understood when looking at a light source, for example a celestial body. If a light source is 100 times lighter than another light source, human vision is unable to notice such difference but only feels that the former is a few times lighter.
Consequently such correction by multiplying constant does not match the perception of human vision.
Also there exist various devices for releasing image signals with varied characteristics. Consequently each output device has been equipped with a printer or a memory exclusive for such device. However an increase in the number of printers in proportion to the increase of the devices for electric information handling is definitely undesirable in consideration of cost and space.
Besides a single device may sometimes release image signals of different characteristics according to the nature of the image to be processed. Consequently fixed image processing may cause inconvenience in such device.